Maine Forest Service warns of Browntail Moth caterpillar infestation

A sample of a browntail moth caterpillar web found in the southern Maine coastal area (photo courtesy of the Maine Forest Service).

AUGUSTA - The infestation of a noxious invasive caterpillar in the Brunswick area is worse this year than last year, and local residents should begin thinking now about how they want to deal with the pest, according to Maine Forest Service (MFS) officials.

Winter web surveys show “extremely high levels of browntail moth caterpillar over-wintering webs in the tops of oak trees” in the Brunswick area, according to a MFS entomologist, under the Maine Department of Conservation. Surveys were conducted in January and February in the southern Maine coastal area from Belfast to south of Portland.

The number of webs in Brunswick, Bath, West Bath, Topsham and Bowdoinham appears to have doubled compared to last year’s number, Charlene Donahue, MFS forest entomologist, said.

Beyond that area, the caterpillar also is showing up in Falmouth, Turner, Augusta and Lewiston “and it may be in other places, and we haven’t found it yet,” she said. “The public needs to be aware of it.”

“I was really hoping the population would go down,” Donahue said, adding that the cause of the increase in the Brunswick area is unknown. “Eventually, they’re going to eat themselves out of house and home, and at some point, the population will crash.”

“This is reminiscent of a similar cycle we went through in the 1990s in the Casco Bay area,” Dave Struble, Maine state entomologist, said. “The public needs to be aware of this situation, and the Maine Forest Service is here to help residents make informed decisions about dealing with the infestation.”

The browntail moth is an invasive species that arrived in the U.S. in the 1910 on nursery stock coming from Europe, moving through Massachusetts, Maine, New Hampshire and Nova Scotia before the population collapsed. The only place where it is now found in North America is the coast of Maine and Cape Cod, Donahue said.
The caterpillar, distinctive because of the two patches of bright orange on its end, contains toxic microscopic hairs on it to keep birds from eating it, “a very good defense system,” the forest entomologist said.

Unfortunately, those hairs can cause a blistery, oozy rash or respiratory distress for human beings who come into contact with them.

The hairs break off the caterpillars and circulate in the air. The caterpillar also molts, and the dried skin containing the hairs can drift, also causing problems for people, Donahue said. The hairs remain toxic for a year or more, so people still can be affected in subsequent seasons, she warned.

Donahue pointed out that there is no single, simple answer as to why and where the browntail moth population is increasing.

“It may be something about the humidity in the area, and the hosts are there,” including oak, apple, crab apple, poplar and birch trees, she said about the web increase. The caterpillar population also may be affected by extreme cold weather and therefore doesn’t appear in Aroostook or Piscataquis counties, she said.

Donahue reported that in Turner, she found an 8-mile-long stretch of trees containing scattered webs. She also noted that while the caterpillar currently isn’t a problem in the Casco Bay area, it has infested the 40-acre Vaughn’s Island Preserve in Kennebunkport, which is heavily used by the public. The moth has been there for four to five years, but hasn’t yet shown up on the mainland, she said. The entomologist said MFS is working with the Kennebunkport Conservation Trust, which manages the area, on the infestation.

The MFS entomologist said that municipalities in the most heavily affected area have been contacted about the infestation. She said it is important for local residents and municipalities to begin thinking now about whether they want to control the browntail moth.

Webs in small trees like crabapple and cherry can be pruned out now and soaked in a bucket of soapy water or burned. For webs in the tops of oak trees, the only control is chemical treatment applied by licensed pesticide applicators who have the equipment to reach the caterpillars.

Pesticide treatment should be done in May, Donahue said. Done any later and neither trees nor people will be protected from the moths, she said.

“This is nothing that a homeowner can control on their own,” she added. “It’s best to work with your neighbors so you can get rid of browntail moths in a larger area.”

The MFS is compiling a list of licensed pesticide companies who are willing to do the work and will make the list available, Donahue said.